1. Field of the Invention
The present invention relates to an optical disk system, and more particularly, to a method and apparatus for controlling an optical output by using a laser diode.
2. Description of the Related Art
In an optical recording/reproducing technique for recording and reproducing data on an optical disk by using a laser, the data is read out by a change in light reflected from the disk. In order to change the reflected light, that is, to record the data on the disk, a compact disk (CD) or a digital video disk (DVD) utilizes the interference between a pit curved inwards from a substrate and a reference surface. A magneto-optical disk uses a method for changing the direction of polarized light of a magneto-optical recording material. Moreover, a phase-change type disk uses a difference between the quantities of reflected light according to the state of a recording material. A CD-recordable (CD-R) disk utilizes a change in an organic pigment. Each disk is classified into a read-only type, a write-once type and an overwritable type. In an optical disk system using such an optical disk, an optical pickup is an essential component to record or reproduce data on the optical disk by controlling an optical output.
FIG. 1 illustrates a conventional laser diode optical output controlling apparatus. The apparatus of FIG. 1 includes a register controller 2, a digital-to-analog (D/A) converter 4, a current driver 6, a laser diode 8, a photo diode 10, and a current-to-voltage (I/V) converter 12.
An optical pickup designer selects digital values suitable for reproducing and recording optical outputs in consideration of the characteristics of the laser diode 8. The digital values are stored in respective registers within the register controller 2. The digital value of the reproducing or recording optical output stored in one of the registers within the register controller 2 is converted into an analog current value by the D/A converter 4, and the analog current value is applied to the current driver 6. The current driver 6 drives the laser diode 8 according to the analog current value. Namely, the current driver 6 amplifies the applied current value to supply reproducing or recording current of a desired value to the laser diode 8. Then the laser diode 8 irradiates a laser beam onto an optical disk (not shown) at a predetermined reproducing/recording optical output level. The laser beam is also irradiated to the monitoring photo diode 10, which is opposite to the laser diode 8. The current of the optical output received by the photo diode 10 is converted into a voltage by the I/V converter 12, and the converted voltage is applied to the register controller 2. The register controller 2 calculates an accurate value by comparing the reproducing or recording optical output with the irradiated optical output only once and stores the calculated value in the register. That is, the accurate value is set by comparing the optical output applied from the I/V converter 12 with the optical output stored in the register only once, and the accurate value is again stored in the register. Thus, the actual optical output of the laser diode 8 is controlled by using the stored value only.
However, during continuous recording, the laser diode generates heat. Therefore, even if constant current is supplied to the laser diode by the register in which a desired value is stored, the efficiency of the optical output of the laser diode is lowered and the optical output of the desired amount is not irradiated. Therefore, sufficient light is not supplied to regions of the disk, and data may be not recorded. Even though data is recorded, the data may not be recorded accurately. Consequently, a carrier-to-noise (C/N) ratio is lowered and the reliability of the recording/reproducing optical disk system is degraded.